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Патент USA US2135979

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Patented Nov. 8, 1938
2,135,979?
UNITED STATES PATENT OFFICE
2,135,979
PREPARATION OF IWIXED ESTERS OF
CELLULOSE
Carl J. Malm, Rochester, N. Y., assignor to East
man Kodak Company, Rochester, N. Y., a cor
poration of New Jersey
No Drawing. Application October 27, 1936,
Serial No. 107,904
6 Claims. (Cl. 260-401)
This invention relates to the preparation of
mixed esters of cellulose containing acetyl
groups and groups of 3-4 carbon atoms in a bath
in which the higher acyl is at least 40% of the
5 total acyl content, to which bath substantially
no propionic or butyric anhydride has been added.
The present invention is particularly directed
to processes employing no more than the usual
proportions of esteri?cation bath to cellulose of
10 like processes in which propionic or butyric an
hydride has been used.
Up to now it has been the general impression
in the cellulose derivative art that to prepare
cellulose acetate propionate or cellulose acetate
1.3 butyrate in the usual esteri?cation bath contain
ing a higher acyl content of more than 40%, that
the use of propionic or butyric anhydride therein
was necessary to obtain a satisfactory product.
For instance, if it was attempted to prepare these
20 esters using acetic anhydride as the only anhy
dride therein, break-down or degradation of the
cellulose would result under ordinary esteri?ca
tion conditions.
In other cases where it has been
attempted to prepare these esters omitting the
25 higher anhydrides in which the pretreating or
presoaking of the cellulose was also omitted, the
esters formed were hazy and gelling of the reac
tion mixture often occurred. To my knowledge,
no one has been able to satisfactorily prepare
30 cellulose acetate propionate or cellulose acetate
butyrate in an esteri?cation in which the acyl
of 3-4 carbon atoms constituted 40% of the
total acyl content of the esteri?cation bath with
out having supplied a substantial amount of pro
35 picnic or butyric anhydride in making up the
bath.
The object of my invention is to provide a
method of preparing mixed cellulose esters con
taining acetyl and propionyl and/or butyryl
40 groups in an esteri?cation bath in which at least
40% of the total acyl is propionyl and/or butyryl
without supplying propionic or butyric anhydride
type referred to, may be prepared in an ordinary
esteri?cation without using propionic or butyric
anhydride, by presoaking the cellulose in not
more than three parts of lower fatty acid to one
of cellulose, at least 40% being acetic acid. At 5
least 1A; part of acid to every part of cellulose
should be employed.
I have found that by this means an adequate
presoaking and activation of the cellulose occurs
so ‘that it is readily susceptible to subsequent 10
esteri?cation and the addition of a higher anhy
dride to the esteri?cation mixture becomes un
necessary to .obtain a satisfactory product. I
have found that by my process in which these
more expensive higher anhydrides may be dis- 15
pensed with, the cost of producing the mixed
esters of cellulose containing substantial amounts
of propionyl or butyryl is considerably reduced
without disturbing the quality of the product
in any way. I have found that propionic acid (or 20
butyric acid) should be used in as large a quan—
tity as possible in the esteri?cation proper, but
yet the amount of this acid, which is employed
in the presoaking, should be limited. Previously,
the fact that the presoaking should have low pro- 25
pionyl and the esteri?cation bath should have
high propionyl was compensated for in preparing
esters having a substantial quantity of propionyl
or butyryl by adding propionic or butyric anhy
dride to the esteri?cation mixture. In order to 30
make up this de?ciency from the absence of pro
pionic or butyric anhydride in the esteri?cation
mixture, a large amount of propionic or butyric
acid should be used to supply propionyl or butyryl
groups and a suflicient amount of acetic anhy- 35
dride to supply the necessary anhydride for ester
i?cation should also be supplied. To increase
the amounts of propionic or butyric acid and of
acetic anhydride, the amount of acetic acid,
which is very necessary to the activation of the 40
cellulose should be limited. I have discovered a
combination in which the acetic acid can be so
thereto and using the same proportion of liquid
to cellulose which is usually employed when pro
45 priom'c or butyric anhydride has been been added.
Other objects will appear herein. Another ob
ject of my invention is to provide a process for
limited and yet give a good activation of the cel
lulose without being present in so large an amount
as to make the supplying of propionic or butyric 45
anhydride to the esteri?cation bath necessary.
making mixed cellulose esters containing acetyl
may be treated with 14-3 parts of lower fatty acid,
containing atleast 40% acetic acid, until the cel
lulose is sufficiently activated. This usually 50
takes place in about four hours at a temperature
of 100-110° F. My invention, however, is not
limited to this particular time and temperature
of presoaking, as the temperature employed
and propionyl and/ or butyryl groups in which the
50 more expensive higher acid anhydrides may be
dispensed with and in which no greater propor
tion of liquid to cellulose need be used than in
processes where it is necessary to supply those
anhydrides.
55
V
I
I have found that mixed cellulose esters, of the
As an illustration of my process, the cellulose
might be even 120 or 130° F. or below 100° F. and 55
2,135,979
2
the time might be either longer or shorter than
four hours, depending a great deal on the tem
perature of treatment. For instance, cellulose
might be moistened with an equal amount of
C21 acetic acid and be kept in an air-tight container
for 12 hours or longer at room temperature in’
order to activate it. In the presoaking of the
cellulosee it is preferred, although not essential,
ing it due to the fairly high temperature of solid
i?cation exhibited by acetic acid. Also, in this
example, the mixture containing anhydride and
catalyst was refrigerated prior to mixing with the
cellulose.
Instead of propionic acid, butyric acid may be
employed in similar proportions with like re
sults.
'
‘
Example II
10
This example illustrates the preparation of a
cellulose acetate butyrate of fairly low viscosity
where a low ratio of liquid to cellulose is em
that this step be carried out in an enclosed con- _, ,
10 tainer so that the full effect of the acetic acid’ is
exerted upon the cellulose without any loss. The
presoaking or activation temperatures may also
be much greater than speci?ed- Forinstance,
temperatures up to LSD-220° F. might be em
ployed.
'
dition permits faster cooling of the presoaked
500 pounds .of cotton was treated with 500
pounds of acetic acid for four hours at 100° F.
800 pounds of butyric acid was then added and the
mixture was cooled to 80° F. A mixture of 1,350
mass due to the presence of additional liquid
and, therefore, saves time in the carrying out of
the process. After cooling the mass to the ex
tent desired, a mixture of propionic or butyric
acetic anhydride and 2,000 cc. of sulfuric acid was
added and the esteri?cation was carried out to a
maximum temperature of 140° F. until a ?rst
ployed in the presoaking, if desired.
After the presoaking, it is preferred to add some
propionic or butyric acid to the mass.
This ad
acid, acetic anhydride and sulfuric acid is added
thereto and the temperature is maintained at the
point desired, depending upon the type of ester
which is being produced. It is desirable that an
acetic anhydride of high concentration be em
ployed, such as 95%, in order to keep the per
centage of acetic acid low in the esteri?cation
30 bath. This becomes more desirable the greater
the proportion of acetic acid to cellulose in the
presoaking. If a high viscosity ester is being pro
duced, it is preferred to refrigerate the mix
ture of propionic or butyric acid, acetic anhydride
and catalyst before adding it to the mass to per
mit proper control of the temperature as de
scribed and claimed in my copending application
Serial No. ‘73,138, ?led April '7, 1936. As an illus
tration of a mixture which may be added, this
mixture may be made up of two mols of pro
pionic acid, one mol of acetic anhydride and a
small proportion of acylation catalyst, depend
ing upon the process which is employed. As will.
be seen by the examples, these proportions are
merely illustrative and may be varied consider
ably within the limits of my invention.
The following speci?c examples illustrate proc
esses of preparing cellulose esters in accordance
with my invention:
Example I
This example illustrates the preparation of a
cellulose acetate propionate of fairly high vis
cosity. A mixture of 400 pounds of re?ned cot
ton linters and 900 pounds of glacial acetic acid
was kept for four hours at 110° F. 860 pounds of
100% propionic acid was added thereto and the
mixture was cooled to 50° F. A mixture of 1,060
pounds of 95% acetic anhydride, 1,100 pounds of
GO 100% propionic acid and 7,200 cc. of sulfuric acid
was prepared and cooled to 20° F. This mix
ture was added to the mixer containing the pre
soaked cellulose and the lower fatty acids induc
ing esteri?cation. The temperature of the re
' action was allowed to rise to a maximum of 80°
pounds of. butyric acid, 1,350 pounds of 95%
stage viscosity of 10 seconds was obtained.
If the cellulose acetate butyrate prepared is to
be’ precipitated without hydroylsis, 200 pounds
of 50% acetic, acid is added. The mass is then
cooled to 100° F. and precipitation is carried out,
as described in my Patent No. 2,030,883. If the
batch is to be hydrolyzed, 600 pounds of 50%
acetic acid is added and the batch is allowed to 30
stand at 100° F. until the desired amount of hy
drolysis takes place after which precipitation may
be carried out, as described in my Patent No.
2,030,883.
'
'
If desired, propionic acid may be employed in
stead of butyric acid in the above example.
Instead of cotton or re?ned cotton linters,
other forms of cellulose may be employed as the
starting material. Re?ned sul?te wood pulp, hav-'
ing a high alpha cellulose content, is an example 40
of a suitable starting material. As may be noted
from the above examples, the proportion of cata
lyst employed may be varied depending upon the
type of ester which it is desired to prepare. Also,
the proportions of propionic or butyric acid may 1
be varied in accordance with the amount of pro
‘pionyl or butyryl which is desired in the product
to be prepared. These proportions may be var
ied as desired, by the individual operator.
As pointed out above, my invention is espe
cially adapted to the preparation of the high vis
cosity esters of the type described due to the
necessity of presoaking in order to obtain uniform
esteri?cation at the temperature necessary to
prepare a high viscosity product. It is only by ;
the procedure which I have discovered that the
addition of propionic or butyric anhydride may
be omitted and yet adequate activation of the
cellulose to prepare the desired product may be
obtained. In general, it may be stated that in pre 60
paring a high viscosity product, the temperature of
the reaction should only be allowed to reach a
maximum of 80° F., while with the regular viscos
ity esters, a maximum of 100-1100 ,F. would be
permissible. The temperature of the low viscosity
The reaction was continued until a dope free
esters may be allowed to rise to a maximum of
from grain and ?ber and having ?rst stage vis
cosity of about 200 seconds was obtained. 1,000
pounds of 50% acetic acid was then added and the
hydrolysis was carried out at 100° F. for about
150° F. The maximum temperature will, of
course, be determined by the particular viscos
ity product which it is desired to produce.
My invention is particularly concerned with
the practical operation of a process of making
cellulose esters. In practical operation the pro
portion‘ of esteri?cation bath to- cellulose is as
low as possible for the sake of economy.‘ Here
tofore when aminimum of esterifying liquid was
F.
10-14 hours or until the desired solubility was
reached.
In a process of this nature in which a low tem
perature is used, it is desirable to add propionic
acid to the cotton-acetic acid mixture before cool
2,135,979
used, dispensing with the propionic or butyric
anhydride in a bath of which 40% of the total
acyl was propionyl or butyrl, was believed to be
3
prises presoaking one part of cellulose in 14-3
parts‘ of a bath essentially consisting of lower
impossible.
fatty acid of 2-4 carbon atoms as the only acid
therein, acetic acid being predominant at a tem
The usual ratio of esterifying liquid to cellu
lose in preparing the low viscosity cellulose esters
in which 40% of the total acyl is propionyl or
perature of approximately 100-110° F., cooling, 5
subsequently inducing esteri?cation by adding a
refrigerated mixture of fatty acid of 3-4 carbon
butyryl is approximately 7:1 while in the case of
the high viscosity cellulose esters it is approxi
10 mately 10:1. It is for these proportions that my
invention is particularly adapted altho it is suit
able for use in esterifying cellulose in which 40%
of the total acyl of the esterifying bath is pro
atoms, sufficient acetic anhydride to induce es
teri?cation, being substantially the only fatty acid
anhydride present and an acylation catalyst, at 10
least 40% of the total acyl in the esteri?cation
bath being fatty acid groups of 3-4 carbon atoms,
pionyl and/or butyryl, the remainder being ace
tyl, with various proportions of bath to cellulose.
In the examples, the ?rst stage viscosity of
the ester is given. This viscosity was determined
as follows:
20 gms. of the esteri?cation dope was weighed
20 out into a 100 cc. beaker and 20 cc. of a mixture
of equal parts by volume of glacial acetic acid
and tetrachlorethane was added thereto. When
the whole was homogeneous and free from lumps,
it was cooled to 25° C. and poured into a 12 mm.
25 diameter tube which was kept at 25° C. The
viscosity was obtained by noting the time (in
seconds) required for a 1A; inch glass bead, weigh
ing .05 gm., to drop thru a 10 cm. column of the
liquid.
30
I claim:
,
l. The process of preparing a mixed cellulose
ester containing acetyl and fatty acid groups of
cellulose acetate propionate which comprises pre
soaking one part of cellulose in 14-3 parts of a
bath essentially consisting of lower fatty acid of
2-3 carbon atoms as the only acid therein, acetic ‘
acid being predominant, at a temperature of ap
proximately 100-110° F., adding propionic acid,
cooling, and subsequently inducing esteri?cation
by adding a refrigerated mixture of propionic
acid, sulfuric acid and sufficient acetic anhydride 25
to induce esteri?cation, being substantially the
only fatty acid anhydride present, at least 40%
of the total acyl in the esteri?cation bath being
propionyl, allowing the temperature to rise to
a maximum not greater than 80° F. and continu
30
ing the reaction until the dope is free from grain
and ?ber.
3-4 carbon atoms which comprises presoaking
5. The process of preparing a high viscosity
one part of cellulose in 1/.;-3 parts of a bath es
cellulose acetate butyrate which comprises pre- ,
35 sentially consisting of lower fatty acid of 2-4
carbon atoms as the only acid therein, acetic
acid being predominant, adding fatty acid of 3-4
carbon atoms, and subsequently inducing esteri?
cation of the cellulose by adding a mixture of
fatty acid of 3-4 carbon atoms, sufficient acetic
anhydride to induce esteri?cation, being substan
tially the only fatty acid anhydride present and
an acylation catalyst, at least 40% of the total
acyl in the esteri?cation bath being fatty acid
45
allowing the temperature to rise to a maximum
not greater than 80° F. and continuing the reac
tion until the dope is free from grain and ?ber.
4. The process of preparing a high viscosity
groups of 3-4 carbon atoms.
2. The process of preparing a mixed cellulose
ester containing acetyl and fatty acid groups of
3-4 carbon atoms which comprises presoaking
one part of cellulose in 14-3 parts of a bath es
sentially consisting of lower fatty acid of 2-4
50 carbon atoms as the only acid therein, acetic
acid being predominant, at a temperature of at
least 100-110° F., adding fatty acid of 3-4 car
bon atoms, and subsequently inducing esteri?ca
tion of the cellulose by adding a mixture of fatty
55 acid of 3-4 carbon atoms, sufficient acetic an
hydride to induce esteri?cation, being substan
tially the only fatty acid anhydride present and
an acylation catalyst, at least 40% of the total
acyl in the esteri?cation bath being fatty acid
60 groups of 3-4 carbon atoms.
3. The process of preparing a high viscosity
mixed est-er of cellulose containing acetyl and
fatty acid groups of 3-4 carbon atoms which com
soaking one part of cellulose in MP3 parts of a 35
bath essentially consisting of lower fatty acid of
2-4 carbon atoms as the only acid therein, acetic
acid being predominant, at a temperature of ap
proximately 100-1l0° F., adding butyric acid, cool
ing, and subsequently inducing esteri?cation by 40
adding a refrigerated mixture of butyric acid,
sulfuric acid and su?icient acetic anhydride to
induce esteri?cation, being substantially the only
fatty acid anhydride present, at least 40% of the
total acyl in the esteri?cation bath being butyryl, 45
allowing the temperature to rise to a maximum
not greater than 80° F. and continuing the reac
tion until the dope is free from grain and fiber.
6. The process of preparing a high viscosity
mixed ester of cellulose containing acetyl and 50
fatty acid groups of 3-4 carbon atoms which com
prises presoaking one part of cellulose in ap
proximately 2%. parts of glacial acetic acid for
four hours at 110° F., adding approximately 2.15
parts of' fatty acid of 3-4 carbon atoms thereto, 55
cooling to 50° F., adding a mixture of acetic
anhydride, fatty acid of 3-4 carbon atoms and
sulfuric acid having a temperature of 20° F. to
the mass, allowing the temperature of the reac
tion to rise to a temperature not exceeding 80° F.
and continuing the reaction until the dope is free
from grain and ?ber.
CARL J. MALM.
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